Field of the Invention
The present invention relates to an image processing technique using a spatial filter.
Description of the Related Art
When performing image forming and outputting an image, local image processing such as spatial filter processing is conventionally performed. This local image processing indicates image processing of performing some calculation using all pixels included in a reference area including a pixel (to be referred to as a processing pixel hereinafter) to be processed. For example, spatial filter processing such as edge emphasis processing or blur processing is performed for digital image data.
Such local image processing may use a method of processing a pixel array at the upper end of digital image data from the left end to the right end, processing the second pixel array from the upper end, and repeatedly executing the same processing up to a pixel array at the lower end. In this method, as the width of the digital image data in the main-scanning direction is larger, a larger memory capacity is required. For example, if an A4-size image is read by a scanner having a resolution of 600 dpi, and converted into digital image data, the digital image data has a size of about 5,000 pixels×7,000 pixels. If, therefore, one pixel has a data amount of 3 bytes (24 bits), a capacity of 5,000 pixels×7,000 pixels×3 bytes=105 MB is necessary to store the digital image data. To reduce a local memory (work area) used for image processing, a technique (to be referred to as band processing hereinafter) of performing image processing by dividing image data into a plurality of bands is generally used.
Furthermore, Japanese Patent Laid-Open No. 11-259646 (patent literature 1) discloses a technique (to be referred to as block processing hereinafter) of dividing digital image data into a plurality of block (tile) areas and separately performing local (vicinity) image processing in order to reduce a memory capacity necessary for image processing.
However, in the band processing or the block processing described in patent literature 1, since there are overlapping areas at the boundaries of the respective areas, if a reference area in the local image processing is widened, the total number of transfer pixels unwantedly increases. For example, if an image in which a blur in an optical system occurs is recovered by spatial filter processing, it is impossible to obtain sufficient recovery performance unless the reference area of the spatial filter is set to have the spread as large as a blur width, as shown in FIG. 19. If, therefore, the blur in the optical system is large, it is necessary to widen the reference area, resulting in an increase in the total number of transfer pixels. Alternatively, if noise in an imaging system is desirably removed by blurring an image by spatial filter processing, it is necessary to widen a blur range as the noise is larger. Therefore, if the noise in the imaging system is large, it is necessary to widen the reference area, resulting in an increase in the total number of transfer pixels.